Coin discriminating apparatus capable of validating coins are known in the art. In such prior art apparatus, test coins are typically directed down a defined path such as a ramp where they pass a number of spaced sensor coils at least one of which is energized to generate magnetic fields. The interaction between the tested coin and the magnetic field generated by the coils enable these apparatus to identify the coin. Specifically, coins having different material compositions and/or sizes will effect the generated magnetic fields differently. A sensing circuit associated with a sensor coil in proximity to the coil generating the field monitors these effects and collects data reflecting changes in the sensed magnetic field. This data can be compared to information stored in memory to determine the denomination and authenticity of the tested coin.
For example, U.S. Pat. No. 4,469,213 and U.S. Pat. No. 4,437,558, which are both hereby incorporated by reference in their entirety, describe a coin discrimination apparatus that utilizes a three-coil stack to identify coins in a manner similar to that described above. The two outer coils of the stack are supplied with identical currents such that magnetic fields are created in the two gaps defined by the three coils. The two outer coils are aligned with the center coil in opposing relation and are similarly energized. Thus, the magnetic fields generated by the two outer coils generally cancel in the region of the center coil, leaving a net electric field of zero (a null) within the center coil.
In use, a sample coin, the type of coin that the discrimination system is intended to accept, is positioned in one of the two gaps between the three coils. As a result, the magnetic field across the sample coin gap is attenuated, thereby preventing a null in the center coil. When a test coin is placed into the discrimination system, it passes through the second gap of the three-coil stack. When the test coin is in the second gap, it attenuates the magnetic field across that gap. If the test coin is identical to the sample coin in the first gap, the attenuation in the opposed magnetic fields will likewise be the same and a null will occur in the center coil. Electronic circuitry is provided to sense the quality of this null to determine whether the test coin matches the sample coin.
U.S. Pat. No. 5,568,855 improves upon the invention of the above-referenced U.S. Patents by providing improved electromagnetic interference protection and by providing a further array of sensors downstream of the identification coils to provide enhanced fraud protection. U.S. Pat. No. 5,568,855 is hereby incorporated by reference in its entirety.
While methods of the above type are generally accurate and effective in performing coin discrimination, certain areas for improvement have been noted. For example, one drawback associated with such methods is that the geometry of the coils in relation to the coin strongly influences the degree of interaction between the coin and the sensor coils. In at least one embodiment of the method disclosed in U.S. Pat. No. 4,469,213, a specific point known as the comparison point on the sample coin is compared to a comparison band along the test coin being passed through the discriminator. The comparison point on the sample coin is the focal point of the circular coils. The comparison band on the test coin, on the other hand, spans a line along the surface of the test coin which is parallel to the descent path of that coin as it passes the comparison point of the sample coin. In other words, whereas in the example shown in FIG. 1, the comparison point 5 of the sample coin would be a relatively specific circular area preferably at the center of that coin, the comparison band 8 on the test coin would be a much larger area spanning the entire length of the coin as it passes through one of the gaps of the sensor coils (represented by the area between the diagonal lines in that same figure).
However, it is possible for the test coin to have a point somewhere along the comparison band 8 that, while not corresponding to the comparison point 5 in location, is nonetheless substantially identical to the material composition of the sample coin at the comparison point 5. This similarity can cause a null that misidentifies the test coin as identical to the sample coin. In other words, if somewhere along the comparison band the test coin appears identical to the comparison point of the sample coin, and if that point of identity is located at a position that does not correspond to the comparison point, a misidentification of the test coin can occur.
Another drawback of prior art designs is that the speed at which successive coins can be processed and identified is limited. One reason for this speed limitation involves the fact that a specific comparison point of a sample coin is being compared to a band on the test coin. Since only a portion of the sample coin is being sampled for the comparison, the travel path of the test coin must be controlled to ensure the test band of a valid coin would include the area of the test coin corresponding to the comparison point on the sample coin. To achieve this goal, coins typically have to be stabilized before they are passed through the gap of the sensor coils. In prior art devices such stabilization occurs by rolling the test coin down a ramped surface thereby preventing the test coin from free falling and ensuring proper alignment with the coils. In some instances, mechanical means are employed to hold the test coin against a reference surface thereby ensuring proper positioning with respect to the sensor coils.
Prior art coin discriminators are also limited in the type of coins they can validate. For example, three coil stack discriminators of the above type are only capable of identifying and accepting one coin denomination at any given time. If the user wishes the coin discriminator to accept other coin denominations, the user must physically open the device and replace the current sample coin with a new sample coin of a different denomination.
In order to overcome this limitation, some prior art apparatus have employed multiple stacks of coils positioned along the test coin travel path wherein each stack of coils includes a sample coin of a different denomination. However, employing multiple sensors in this manner increases the time needed for the microprocessor to identify a test coin, thereby increasing the delay time needed before the next test coin can be considered.
As mentioned above, some prior art discriminators are susceptible to electromagnetic interference from outside sources. If such discriminators are exposed to outside sources of electromagnetic energy, then a satisfactory null may not exist in the center coil despite the fact that the test coin and sample coin are identical.
The above characteristics of existing coin discriminators limit performance criteria such as: coin feed rate, coin identification accuracy (including susceptibility to outside electromagnetic interference), and the number of different coins that can be accepted without modification at any given time. These characteristics are crucial for machines such as gaming machines in which coins are inserted at a very fast rate.